Production of non-earing molybdenum sheet



United States Patent 3,324,699 PRODUCTION OF NON-EARIhlG MQLYBDENUM SHEET Ronald L. Barto, Wicklilfe, Ohio, assignor to General Electric Company, a corporation of New York No Drawing. Filed Jan. 4, 1965, Ser. No. 423,306 3 Claims. (Cl. 72365) This invention relates to a process for the production of molybdenum sheet having no more than a minimum degree of directionality of mechanical properties such that it is not subject to the phenomenon of caring during working operations including deep-drawing as are molybdenum sheets not produced according to the invention.

Directionality of physical and mechanical properties in commercial alloys results from crystallographic preferred orientation and from the alignment of stringers of second phases, impurities and microcracks, or from both causes together. Such directionality of properties can be beneficial such as in steels intended for electrical and magnetic applications in which certain crystal orientations lead to desirably higher magnetic permeability. However, in sheet metals intended for forming applications, especially for working by deep-drawing or other similar processes, if the sheet metal has a significant directionality of mechanical properties, an even number of cars or scollops will form around the periphery of the sheet being drawn, or will remain at the top of the cup if the drawing is completed without leaving a flange. Each ear represents a direction in which resistance to deformation was slightly lower relative to the rest of the sheet. The height of the cars is directly proportional to the degree of preferred orientation in the blank that was used to draw the cup. In addition to the extra expense caused by the requirement of trimming off the ears in many applications, the sheet metal in the region of the ears which has been elongated more than that of the rest of the sheet is also thinner than the rest of the sheet and therefore weaker. Furthermore, if caring is severe enough, the metal may split in the region of the ears, either during the drawing operation or in subsequent forming operations or in service.

It is well known that preferred orientation can be controlled to a certain extent by controlling the interrelations of mechanical working, temperature and recrystallization. Many schemes have been proposed which purport to tbe applicable to various metals for the control of preferred orientation and for the elimination of earing, however, earing is a complex phenomena depending on directionality of mechanical properties in general, including texture, fibering impurity distribution and other factors in addition to preferred orientation. Therefore, extant theories concerning the control of preferred orientation are not necessarily directly applicable to its control in a specific metal such as molybdenum. This is even more particularly so since molybdenum is generally brittle in a recrystallized condition and is generally used in a col-d worked condition. Since many theories on the control of preferred orientation require that the product be in a recrystallized condition, those theories are not directly applicable to molybdenum.

It is an object of the present invention to provide molybdenum sheet having a minimum degree of directionality of mechanical properties.

Another object of the invention is to provide such sheet which can be utilized in deep-drawing operations without deleterious ean'ng.

Briefly stated, the present invention in one embodiment provides a process for the production of molybdenum sheet having minimum directionality of mechanical properties. Molybdenum sheet, identified herein as a first body, is first rolled in one direction in a warm-working temperature range for a total reduction of 50 to (preferably about 65%) in thickness to form a second body. The cold Worked material is then recrystallized. Rolling is continued in the same direction fora reduction in thickness of from 65 to (preferably about 75%) below the second body to form a third body. The material is then recrystallized a second time. The sheet then is turned degrees in the plane of the sheet and rolled for a reduction in thickness of about 50% (45-55%) below the third body to form a fourth body. The sheet is again turned about 90 degrees, going back to the original direction of rolling and rolled to a total reduction in thickness of 65 to 80% (preferably about 72%) below the third body to finish size. This will leave about 6580% reduction in thickness cold work (preferably about 72%) in the final sheet, representing the deformation given to the third and fourth bodies since the last recrystallization. The rolling of the fourth body can be done at temperatures lower than used for the other bodies. Warm-working is used in the steps following recrystallization. For developing desirable properties in the product, a final stress relief anneal in the temperature range of 900975 C. is used. Temperatures which may be used for warmworking depend on the amount of prior deformation that the material has sustained since the last previous recrystallization, but generally is within the temperature range of 900-1200" C. Warm-working is defined as deforming a metal at a temperature high enough to significantly lower stresses but not so high as to cause recrystallization. The temperature range in which warm-working can be performed depends somewhat on the amount of work-hardening present in the metal. Recrystallization of the cold Worked material is accomplished at a temperature of 1350 C.: +-l00C. (-l2591450 C.). It is desirable to have about 65-80%, or preferably about 72% cold work in rolled molybdenum sheet.

The present invention applies to the production of molybdenum sheet, which means sheet which is essentially pure molybdenum in the context of the invention. In other words, the molybdenum should not include alloying elements of a type or in amounts such as to nullify the advantages of the invention in producing non-caring sheet. Generally speaking, dilute solid solution alloys would be expected to behave in the same manner as does unalloyed molybdenum when they are processed according to the invention. Alloys containing second phases in more than rather small amounts would not be expected to display the advantages of the invention. Although powder metallurgy was used to produce the molybdenum rolled in the empirical investigations leading up to the present invention, the invention is equally applicable to arc-cast molybdenum sheet.

Typical room temperature properties of unalloyed molybdenum sheet produced according to the invention are tabulated in Table I below along with the results of Tinius Olsen Cup Depth testing. In the Olsen cup test, a plunger with a ball tip is used to form a cup in the sheet. The depth of the cup is a measure of ductility under biaxial stress and serves to augment other methods used to measure ductility such as tensile elongation and bend testing. The table presents the data for various final thicknesses of sheet produced according to the invention. T. S. (p.s.i.) means tensile strength in pounds per square inch;

0.2% yield means the 0.2% offset yield strength in pounds per square inch; the percent elongation was measured in a 2 inch gage length.

TABLE I.-TYPICAL ROOM TEMPERATURE PROPERTIES Measurements were made of the variation of wall thicknesses of cups drawn from sheet produced according to the invention in comparison with cups made from sheet prepared by conventional techniques. The cups had outside diameters of about 1.375 inches and depths of about 0.75 inch. The variations were measured at different radial angles around the circumferences of the cups. The normal molybdenum sheet had a nominal thickness of 0.0301 inch and a range of wall thickness variation of 0. 0013 inch. The sheet produced according to the invention had a nominal wall thickness of 0.0292 inch with a range of wall thickness variation of only 0.0001 inch. Thus, it is seen that there is a far smaller variation in the wall thickness of sheet produced according to the invention than in normal molybdenum sheet, due to the lack of caring in sheet produced according to the invention.

The tensile properties of conventional molybdenum sheet and sheet produced according to the invention were also tested as a function of angle from the final rolling direction. It was found that the ultimate tensile strength of conventional sheet varied an amount of 21,000 p.s.i. as a function of direction or angle while that of sheet of the invention varied only 4,000 p.s.i. The 0.2% offset yield strength varied 15,500 p.s.i. for conventional sheet, but only 2,500 p.s.i. for sheet of the invention. The tensile elongation in one inch varied 19% in conventional sheet and only in sheet of the invention. These data demonstrate a great reduction in directionality of mechanical properties in sheet made according to the invention over conventional molybdenum sheet.

An example will now be given of a specific process used to produce unalloyed molybdenum sheet according to the invention having a final thickness of 0.040 inch.

A one inch thick ingot was rolled in one direction in increments of about 20% in the temperature range of 900- 1200 C. to a thickness of 0.327 inch and then recrystallized in the temperature range of 12501450 C. for times ranging from /2 hour to minutes. Rolling was continued in the same direction and temperature range in increments of preferably about 510% to a thickness of 0.140 inch, at which thickness the material was again recrystallized in the same manner. The material was then turned 90 degrees in the plane of the sheet and rolled in the same manner to a thickness of 0.080 inch. The rolling direction was then changed back to the original and the sheet rolled in the same manner to a thickness ogf 0.040 inch. Finally, the sheet was stress relieved for one hour in the temperature range of 900975 C.

4 1. In a process for the production of molybdenum sheet having minimum directionality of mechanical properties, said process involving rolling from a first body, the steps comprising sequentially:

(A) rolling said first body in one direction within the range of warm-working temperatures for a total reduction in thickness of 50% to 80% from said first body to produce a second body;

(B) recrystallizing said second body;

(C) rolling said second body in said one direction within the range of warm-working temperatures for a total reduction in thickness from said second body of about from 65% to 85% to produce a third body;

(D) recrystallizing said third body;

(E) rolling said third body in another direction approximately 90 degrees in the plane of the body from said one direction within the range of Warm-working temperatures for a total reduction in thickness from said third body of about 45% to 55% to produce a fourth body;

(F) rolling said fourth body in said one direction which is at about 90 degrees in the plane of the body from said another direction for a total reduction in thickness from said third body of about 65% to 80% to the final thickness.

(G) stress relieving said sheet of said final size.

2. The process of claim 1 in which the warm-working temperatures are in the range of about 900-1200 C. and recrystallization is done in a temperature range of 12501450 C., and stress relieving is done in the range of 900-975 C.

3. A process for the production of molybdenum sheet I having minimum directionality of mechanical properties,

While specific examples have been given of the process said process involving rolling from a first body, the steps comprising sequentially:

(A) rolling said first body in one direction at warmworking temperatures within the range of about 900- 1200 C. for a total reduction in thickness of about 65 from said first body to produce a second body;

(B) recrystallizing said second body at a temperature in the range of 12501450 C.;

(C) rolling said second body in said one direction at warm-working temperatures within the range of about 900-1200" C. for a total reduction in thickness from said second body of about to produce a third body;

(D) recrystallizing said third body at a temperature in the range of 12504450 C.;

(E) rolling said third body in another direction approximately degrees in the plane of the body from said one direction at warm-working temperatures Within the range of about 9001200 C. for a total reduction in thickness from said third body of about 50% to produce a fourth body;

(F) rolling said fourth body in said one direction which is about 90 degrees in the plane of the body from said another direction a total reduction in thickness from said third body of about 72% to the final thickness;

(G) stress relieving said sheet of said final thickness in the temperature range of 900975 C.

References Cited UNITED STATES PATENTS l/ 1960 Schnitzel et al 72700 5/1962 Frank et a1 72-700 

1. IN A PROCESS FOR THE PRODUCTION OF MOLYBDENUM SHEET HAVING MINIMUM DIRECTIONALITY OF MECHANICAL PROPERTIES, SAID PROCESS INVOLVING ROLLING FROM A FIRST BODY, THE STEPS COMPRISING SEQUENTIALLY: (A) ROLLING SAID FIRST BODY IN ONE DIRECTION WITHIN THE RANGE OF WARM-WORKING TEMPERATURES FOR A TOTAL REDUCTION IN THICKNESS OF 50% TO 80% FROM SAID FIRST BODY TO PRODUCE A SECOND BODY; (B) RECRYSTALLIZING SAID SECOND BODY; (C) ROLLING SAID SECOND BODY IN SAID ONE DIRECTION WITHIN THE RANGE OF WARM-WORKING TEMPERATURES FOR A TOTAL REDUCTION IN THICKNESS FROM SAID SECOND BODY OF ABOUT FROM 65% TO 85% TO PRODUCE A THIRD BODY; (D) RECRYSTALLIZING SAID THIRD BODY; (E) ROLLING SAID THIRD BODY IN ANOTHER DIRECTION APPROXIMATELY 90 DEGREES IN THE PLANE OF THE BODY FROM SAID ONE DIRECTION WITHIN THE RANGE OF WARM-WORKING TEMPERATURES FOR A TOTAL REDUCTION IN THICKNESS FROM SAID THIRD BODY OF ABOUT 45% TO 55% TO PRODUCE A FOURTH BODY; (F) ROLLING SAID FOURTH BODY IN SAID ONE DIRECTION WHICH IS AT ABOUT 90 DEGREES IN THE PLANE OF THE BODY FROM SAID ANOTHER DIRECTION FOR A TOTAL REDUCTION IN THICKNESS FROM SAID THIRD BODY OF ABOUT 65% TO 80% TO THE FINAL THICKNESS. (G) STRESS RELIEVING SAID SHEET OF SAID FINAL SIZE. 